Pulse generating circuit



Feb. 4, 1947.

D. E. MAXWELL PULSE GENERATING CIRCUIT Filed June 19, 1944 n W :e $1 M. x P ta 0 n HW x W TR QGER Pl/L 82 SOURCE TRIGGER PULS E SOURCE TRIGGER PUL 5E Patented Feb. 4, 1947 2,415,302 PULSE GENERATING cmcorr Donald E. Maxwell, Syracuse, N. Y., assignor to General Electric Company, a corporation of New York Application June 19, 1944, Serial No. 541,042

My invention relates to electric pulse generating circuits, and more particularly to means for 11 Claims. (01. 250-27).

afiected by the energy stored in the inductive eircuit at the end of each pulse. This problem is commonly encountered when the output of a pulse generating circuit is utilized to modulate the high frequency oscillations of a magnetron oscillator. In such a circuit a pulse transformer or simp1y a charging reactor is commonly interposed between ,the pulse'generator and the magnetron oscillator tube. When a transformer is used it servesboth to increase the voltage applied to the magnetron and to provide a charging path for the capacitive pulse-forming energy storing element. Since the reactor or transformer and the load circuit ordinarily include a certain amount of stray and distributed capacitance, it is found that at the termination of each pulse the energy stored in the conductive circuit elements has a tendency to initiate transient high frequency oscillations in the resonant circuit comprising the transformer or reactor and the stray and distributed capacities. Such high frequency oscillation at the trailing edge of a rectangular voltage pulse is objectionable for a. number of reasons. In the first place, the inversevoltage peaks produced by the oscillation add to the charging voltage of the pulse-forming element thereby tending to produce arc-over of the pulse triggering tube. Another objectionable feature of the trailing edge oscillation is that the voltage peaks of polarity similar to that of the desired pulse tend to'start oscillation of the magnetron tube in undesired spurious modes. s

V Commonly, trailing edge oscillations of the character described are damped by diode clipper tubes connected across the pulse load circuit in such a manner that they are non-conductive for the desired pulse voltages, but conduct inverse oscillation voltages, thereby to dissipate the stored energy. Such clipper tubes, however, are. large and expensive, because they must withstand the full pulse voltage in the non-conductive direction,

' must be capable of conducting high peak cur.-

rents, and because they require appreciable heat dissipating capacity to dissipate the considerable stored energy in the pulse transformer or charging reactor.

Accordingly, it is an object of my invention to provide new, and improved means for shaping the trailing edge of voltage pulses to provide more nearly rectangular pulse wave shapes.

It is a further object of my invention to provide new and improved means for suppressing undesired-high frequency oscillations at the trailing edges of electric pulses.

It is a still further and more specific object of my invention to provide non-linear inverse feedback means for suppressing trailing edge oscillations at the termination of voltage pulses.

It is a particular object of my invention to provide low current, diodedamping circuit for suppressing trailing edge oscillations in high voltage pulse generating circuits.

Briefly, in accordance with my invention, unilateral conducting means, such as a diode or other electron discharge device, is connected for response to voltage oscillations across a pulse load circuit in'such manner that the oscillations are fed back in inverse phase relation to the input of the pulse triggering tube, thereby to suppressthe oscillations.

My invention itself will be more fully understood and its objects and advantages further appreciated by referring now to the following detailed specification taken in conjunction with the accompanying drawing, in which Figs. 1 and 2 are schematic circuit diagrams of pulse generating circuits embodying my invention in one form; Fig. 3 is a schematic circuit diagram of a pulse generating circuit embodying myinvention in another form; and Fig. 4 is a graphical representation of various pulse wave shapes illustrating the operation and effect of my invention.

Referring now to the drawing, and particularly to Fig. 1, I haveshown a pulse generating circuit comprisinga source I of substantially rectangu- ,by', positive voltage pulses from the source I, there.-

ing circuit also includes a high resistance H and. I

a source of unidirectional electric potential, such as a battery i2, connected in series circuit relation between the anode and.cathode oftheelectron discharge device 3. :The cathode 5 of the discharge device 3 and the negative terminal of .toground. "Ijhis capacitance.isindicated hydotted lines 11 in Fig. 1 as capacitance'between ithe -a i'1ode .ancl.c.athode of thema gnetrontube 9. The stray and ,distributed capacities represented by 4 the full voltage of the condenser 1' is impressed across th reactor 8 and the magnetron 9.

The inductance of the charging reactor 9 is made sufficiently great that comparatively littlecurrent flows through the reactor during the pulse period. During the pulse, however, a small amount .of current is graduallyibuilt. up in the: reac tor i so that, at thelterrninationiof the pulse a certain amount of energy is stored in the re-- actor. At the termination of the pulse discharge this stored energy tends to initiate an oscillatory charge anddischarge of the distributed and stray th lcapacitor fll iorm with the charging reactor 7 8 a resonant ,circuit havin a high natural fref lti gy .ofqoscillation with respect to ,the repetition rate {of the pulses from the source I. For

,the ,chalgihg reactor circuit shown this atural frequency of oscillation is.ordinari1y,of'the order of. 100, kilocycles per second. rrnepiiise repetition rate, on ,the other hand is ordinarily ofthe order of 5.0.0= to5il00 pulses per-second in radio detection apparatus ,or pulse communication,apparatus.

For "the u os of uppressing osc llations in \the tuned circuit 8, .l l. at the termination of each pul e, I .provide a non-linear inverse fe edback circuit comprising a diode rectifier |8ponnected between ;the output and input circuits of the pulse triggering tubes, More specifically, the anode ,l8a.,.pf -the diode I8 is connected, to .the cathode .915 of thema netron :9 and the cathode [8b of the diodel 8 is connected to the control electrode 6 or th discharge device .3 7 through. the couplin .l s cha 11ged }to substantially the full voltage of .t pr sing the resistorzll, the condenser I, and the lchargingzinductor 8. The voltage pulses. applied 7, 'rrornsthe source I through the transformer 2 tterv 1:2 throu t e c ar in circuit omrecurrentlyand periodically impress positive potentials1-upon thecontrol electrode' fi for predetermined pulse intervals, thereby to render the discharge device-3 conductive for such intervals.

v lhenthe'discharge device 3 becomes conductive, the condenser "I discharge throughthe discharge deviceS and the load circuit-comprising the magnetron oscillator tube:9 and the charging reactor "The olta e drop "thr u h hed fscha e d vice"3' is relatively small, so that substantially capacitance rep-resented by the condenser H. In

the, .absenceiofuthe. feedback circuit through the diode rectifier l8,.this oscillation would cause a fluctuation of voltage across the reactor 8 and magnetron 9' in the manner illustrated by the lof'the pulse'tfi of Fig. 4"in'the'rnanne r of the In suppressing the trailingedge oscillations, the diode rectifier 18 functions in the following manner. ,During..the pulse interval ,.the cathode 53b of the magnetron 9. is negative'with respect to the grounded anode Ba, so that 'theanode iBa of the diode i8 is negative with respect to ground. At the sametimethe triggering pulse on the secondary winding E3 of the transformer 2 raisesythe cathode 18b of the rectifier 18 to a potential positive with respect to ground. "Accordingly, during the pulse intervaLthe rectifier [8 remains. nonconductive. At. the termination Of'thfi pulse, and as soon as the energy stored in the reactor 8 'el'ifects a reversal of voltage across the magnetron a, the. anode 13a of the rectifier ,|8,is driven positive with respect to ground. Atlthistime, the

. control electrode ter the 'triggeringfdischarge de-.

vice -3, The grid potential oi the discharge device- 3 lS tl'1LlS raised from'below cutoff to some value at which conduction again'takes plac 01- tends.

to take place. Conduction through the tube 3: impresses acrossthecharging reactor'8 and mag-, netron-Q .a voltage opposed to thepositive oscillatiorl voltage initiating discharge through the rectifier it. As a result of this action, there occurs a very effective damping of the positive 7 voltage pealgs'across the magnetron :.9.

It is .believed that, inoperation, Tthe positive voltage fed back throughthe diode rectifierflu to the grid of .thefdischarge device ,3 will ever reach a value sufiicientgtoov'ercojnle thehFegative bias upon the control electrode 6 before complete damping of ,the positive j voltage swing across ,the ch'arging reactor .8 vis effected; Therefore,

substantially no power is supplied to the control electrode 6 of the discharge device ,..3 land the current through. the ,diode rectif er 8 will .be. very low; AccordingIy;' the diode rectifier 18. maybe a tube of small peak current rating. in contrast 'to the high peak vemissivity ,and' large .heat .dis sipating capacity required for. ,a .diode. damper tube connected across the electrodes ofthe ma netronS. I 1' It will be noted from 'Ei'ggl that the cathode l8b.of the diode rectifier I8 is not at ground po- 'tential. Accordingly when the 'eathode lab. is

provided'with a heater, the heater will not beat vlde a very low capacity filament winding in order to avoid shunting the trigger pulse source. -1At Fig. 2 1 haveshown an alternative arrangement for energizing a cathode heater of the diode rectifier l8. Inthe circuit shown at,Fig.. 2, the cathode heater |8c is supplied from a suitable source of alternating current supply 22 through a double secondary winding 3a on the trans former 2. In all other respects the circuit of Fig. 2 is similar to that of Fig. 1. y

1 At Fig. 3, I have shown a further embodiment of myinvention wherein the non-linear inverse feedback circuit is so arranged that the diode rectifier therein need not'withstand the full pulse voltage in its non-conductive direction. In accordance with the modification of Fig. 3, the feedback diode may be a small receiver-type tube having both low peak-current and low peak-voltage-rating. 'f Referring now more particularly to Fig. 3 of the drawing, I have shown a source 25 of triggeringpulses arranged to supply, through a transformer 26, positive potentials to the control electrode 21 of an electron discharge device 28 having an anode 29 and a grounded cathode 30. The anode 29 of the discharge device .23 is connected through the primary winding of a coupling transformer 3| to a suitable source of positive potential indicated upon the drawing as B+. By way of specific example, the positive potential source B+ may be of the order of 2500 volts. The control electrode 21 of thedischarge device 28 is biased negatively from a suitable source of negative po tential B- which is connected through aresistor 3-2 -to one terminal of the, secondary winding of the coupling transformer 26. With the assumed positive potential of 2500 Volts upon the anode 29of the discharge device 28, the negative biasing potential from the source B may suitably be of the order of 200 volts, a Thesecondary winding of the coupling transformer 3| is connected between the control electrode 33 and the grounded cathode 3,4 of a second electron discharge device 35 through a coupling capacitor-36. The control electrode 33 of the discharge device 35 is biased negatively from the potential source B- through the secondary winding of -the coupling transformer 3|. A resistor 31 is connected across the secondary winding of the coupling transformer 3| to provide a fixed load on the transformer during the non-conducting period of the device 28. V {The discharge device 35 corresponds to the pulse triggering discharge devices 3 of Figs. 1 and 2 and includes an anode 38 connected through a charging resistor 39 to a suitable source of positive unidirectional electric current supply B|+. In-conformity with the voltage values hereinbefore specified by way of example, the potential source Bl may supply approximately 5000 volts. 'A capacitive pulse-forming energy storing element shown as a condenser 40 is connected through the discharge device 35 to a load circuit comprising an autotransformer 4| and-a magnetron oscillator 42 having an anode 42a and, a cathode 42b. The condenser 40 is connected across the primary winding of the transformer 4| through the discharge device 35, and the magnetron' oscillator 42 is connected across the secondary winding of the transformer 4|, the anode 42a of the magnetron being grounded. In conformity with the. voltage values heretofore mentioned by way, of example, the pulse: voltage across thesecondary winding of, the. transformer of Fig. 4. With the addition of the inductor 4 4,

6 4| maybe. of the order of 12,000vo1ts. 'As in' the embodiment of my invention illustratedat Figs. land 2, the stray and distributed capacitanceof the load circuit isillustrated by dotted lines at 43 as a capacitance connected across the primary winding of the autotransformer 4| of Fig. 3.

At Fig. 3, I have shown an inductive reactor 44 connected in parallel circuit relation with the primary winding of the autotransformer 4|. While the reactor 44 forms. no part of my present invention,it is useful in adapting the pulse generating circuit for the formation of very short pulses of lesser duration than those for which the transformer 4| is in itself designed. In operation, the reactor 44 augments the energy storing capacity of the pulse transformer 4 l, thereby to increase the tendency of the stored inductive energy in the load circuit to initiate high frequency oscillations at the termination of each pulse. The transformer establishes very high frequency oscillations which are interposed upon the oscillations set up by the reactor 44. The stored energy of these elements is useful to a certain degree in eifecting a rapid decay of voltage at the termination of a desired pulse, but continuing oscillations after the voltage across the primary winding of the autotransformer initially decays to zero are undesirable.

For the purpose of suppressing such continuing oscillations, I provide a non-linear inverse feedback circuit comprising a diode rectifier 45 01 other suitable electron discharge device having its anode 45a grounded and its cathode 45b connected to the ungrounded end of the primary winding of the autotransformer 4| through a current limiting'resistor 46. The cathode 45b of the diode rectifier 45 is also connected to the control electrode 21 of the discharge device 28 through a coupling capacitor 41 and the secondary winding, of the couplin transformer 26.

In operation of the pulse generating circuit shown at Fig. 3, positive voltage pulses generated at the source 25 are applied to the control electrode 21 and render the discharge device 28 conductive for predetermined pulse intervals.

-The pulses are amplified in voltage in the 'discharge device 28 and applied with positive polarity through the transformer 3| to the control electrode 33 of the pulse triggering discharge device 35. ,The positive triggering pulses from the transformer 3| render the discharge device 35 conductive during the predetermined pulse intervals, thereby to permit pulse discharge of the capacitor 40 through the magnetron tube 42, the pulse transformer 4|, and the inductor 44, H Between pulse intervals, the capacitor 40 is re-. charged from the potential source B|+ through the charging resistor 39, the inductor 44, and the primary winding of the pulse transformer.

If it is assumed, by way of example, that the reactor 44 is omitted and that the generated pulses are of shorter duration than those for which the transformer 4| is itself designed, the voltage'decay atthe terminationof each pulse would be gradual, as indicated by the curve 59 however, to increase the energy stored in. the resonant circuit during each pulse, the voltage, decay at the termination of each pulse is more rapid, but also becomes of an oscillatory nature, as indicated by the curve l9 of Fig. 4. The nonlinear inverse feedback circuit through the diode rectifier suppresses positive or inverse voltage peaks of the oscillatory discharge, thereby to shape the trailing ed e of t e. P lse. ifllgtifisii in the manner of the full line curve 21.. Iherati tidnof the non-linear fee'dbackccircuitsori Fig. 33 will: be evident :ifrom the followingaexplanation- During the pulse, the. negative voltage across. the primary 'windingcofi theuautotransformer 411 applies a negative potential to thezcathode45b of the diode 45, so that the 'diodeiconductsq, The diodelcurrent is limited to a suitable value by the resistor 46;. It will be observed that during the pulse interval, with the diode .45 conducting, the relatively small voltage dropacross the diode 45 introduces a small amount of negative feed back to the control electrode 21 of the discharge device 28 through I the coupling capacitor 4-1. This negative feedback, however, is unobjectionable because the amplitude of the positive pulses from the source 25 is sufficient to render the discharge device 28 conductive despite the negative feedback. 1 r

At the trailing edge of eachpulse, nothing of consequence occurs until-the voltage across the primary winding of the autotransformer 41 re: verses and becomes positive. As soon as such voltage reversal takes place, the diode 45' becomes non-conducting, When the; diode '45 ceases conduction, the total positive voltage across the primary winding of the autotransformer 4! appears across the resistor 46 and. the resistor 32 in series, since the capacitor 41 offers substantially no impedance for oscillation voltage of the frequencies here involved. Since the voltage of oscillations across the primary winding of the autotransformer M are of great intensity compared to the bias voltage from the source B- the proportionate part of the oscillation volt.- age appearing across the resistor 32 is sufiicient in; intensity and of proper polarity to render or tend to render the discharge devicev 28 momentarily. conductive when the voltage across the primary winding of the autotransformer 4| swings positive. As soon as theldischarge device 28'bec0mes conductive, a. positivegpotential is placed upon the control electrode 33 of the dischargeidevice .35 thereby to render the device 35 conductive and permit discharge of the condenser through the autotransformer primary winding. The discharge voltage opposes the positive oscillation voltage, thereby to prevent buildup of the oscillations. By so suppressing positive voltage peaks, the shape of the trailing edge of the pulse 20 of Fig. ,4 is constrained to follow the curve 2!. It will be noted, of course, that since the netrvoltage across the primary winding of the autotransformer ill does not actually become negative as a result of feedback through the coupling capacitor 41, the magnetron oscillator 42 remains noneconductive after it is shut on by the initial voltage decay.

From the numerical exampleof voltage values given throughout the above description of Fig. 3, it, will be noted that the voltage applied to the rectifying diode 45 at no time even approaches in intensity the voltage appearingacross the secondary winding of the autotransformer 41. When the output Voltage of the autotransformer 4] is of the order of 12,000 volts, as mentioned hereinbefore by way of examplethe'diode 4-5 may have peak inverse voltage rating, of the'order of 1000 volts;

While I have described, by way of example, only certain preferred embodiments of my invention, many modifications will occur to those skilledin the art, and I therefore wish to have it understood that I intend in the appended claims to cover all'such modifications as fallw'i'thln the true spir'itand scope of my inventions 5 What-I :claim as new and desire :to securezby Letters Patent of the United'States is? 1. In combination, an electron dischargesdevice including ananode, acathodeand a control electrode, means including saidcontrol electrode for recurrently rendering said discharge device 0011 ductive for predetermined pulse intervals, a" ca pacitive pulse-forming energy storing element, "a load circuit connected to said capacitive element through said discharge device, said load circuit in cluding an inductive energy storing element hav; ing a tendency to initiate voltage oscillations across said load circuit at 'thetermination of each of said pulse intervals, and means'for suppressing said oscillations including unilateral conducting means connected between'said load cir'cuitahd said control electrode to render said discharge device conductive in response to a reversal of vo'lt ageacross said load circuit. v 2. In combination, an electron discharge device includin an anode, a cathode, and a control-electrodegmeans including saidcontrol electrode for recurrently rendering said discharge device'conductive for predetermined pulse intervals, a ca pacitive pulse-forming energy storing eleihen'tfa load circuit connected to said capacitive'element through said discharge device, said load circuit having impressed thereon recurrent voltage pulses of one polarity and including an inductive energy storing element having a tendency to initiate voltage oscillations across said load circuit at' the termination of each of said pulses, andmeahsfor suppressing said oscillations including unilateral conducting means connectedbetween said-load circuit and said control electrode to rendersaid discharge device conductive in response to volt ages of opposite polarity across said load circuit.-

3. In combination, an electron'dischargedevice including an anode, a cathode, and a control electrodemeans including said control electrode for recurrently rendering said discharge device conductive for predetermined 'ipulse intervals, "a capacitive pulse-forming energy storing 5 elmentya load circuit connected to said'capaci'tive element through said discharge deviceysaid load'circuit including an inductive energy storing element, and unilateral conducting means'connected be tween said load circuit and said control electrode to render said discharge device conducti've in responseto Voltage oscillations'in sajid load cir cuitinitiated by said inductiveelement at the termination of each'pulse intervals 4. In combination, an electron discharge device including an anode, a' cathode, and a control electrode', means: including said controlelectrode-for recurrently rendering said unsung-enemas con ductive for predetermined pulse intervals,- a "capacitive pulse-forming energy storing le'mene a load circuit connected to said capacitive element through said discharge device, 'saidload circuit including an inductive energy storing element having a. tendency to initiate voltage Eoscillatibns across said load circuit at the termination or 'each of'said pulse intervals, and means including'a unilaterally'conducting device for supplying said oscillations to said control?electrode'therebyiito render said discharge device conductive -to*supress'said oscillations. I i

5. In anel'ectrici pulse generating circuit-in cluding a resonant-load icircuit'and an electron discharge device having a control electrode, means including said control" electrode; for rendering said discharge device-conductive for predetermined pulse intervals, andlmans for sll-ppressing natural frequencyruminations-insaid 9 load circuit at the termination of said pulse intervals comprising unilateral conducting means connected between said resonant circuit and said control electrode to render said electron discharge device conductive in response to said oscillations.

6. In an electric pulse generating circuit including an energy storing load circuit having a tendency to initiate natural frequency oscillations and an electron discharge device having a control electrode, means including said control electrode for rendering said discharge device conductive for predetermined pulse intervals to provide in said load circuit voltage pulses of one polarity, and means for suppressing said natural frequency oscillations at the termination of said pulse intervals comprising unilateral conducting means connected between said load circuit and said control electrode to render said electron discharge device conductive in response to voltages of opposite polarity in said load circuit.

'7. In combination, an electron discharge device including an anode, a cathode, and a control electrode, means including said control electrode for recurrently rendering said discharge device conductive for predetermined pulse intervals, a capacitive pulse-forming energy storing element, a load circuit connected to said capacitive element through said discharge device, said load circuit including an inductive energy storing element having a tendency to initiate voltage oscillations across said load circuit at the termination of each of said pulse intervals, and means for suppressing said oscillations comprising unilateral conducting means connected to supply said oscillations to said control electrode.

8. In an electric pulse generating circuit including an energy storing load circuit having a tendency to initiate natural frequency oscillations and an electron discharge device having a control electrode, means including said control electrode for rendering said discharge device conductive for predetermined pulse intervals, and means for suppressing said natural frequency oscillations at the termination of said pulse intervals comprising unilateral conducting coupling means between said load circuit and said control electrode, said coupling means being connected to remain substantially inefiective during said pulse intervals.

9. In an electric pulse generating circuit, an electron discharge device having a control electrode, a load circuit including an inductive element, means for rendering said discharge device recurrently conductive for predetermined desired pulse intervals, said inductive element having a tendency to initiate electric oscillations in said load circuit at the termination of each pulse, and coupling means including a unilateral conducting device connected between said load circuit and said control electrode, said unilateral conducting device being disposed to render said coupling means substantially non-responsive to desired pulses in said load circuit.

10. In an electric pulse generating circuit, an electron discharge device having a control electrode, a load circuit including an inductive element, means for rendering said discharge device recurrently conductive for predetermined pulse intervals to establish in said load circuit a succession of voltage pulses of one predetermined polarity, said inductive element having a tendency to initiate electric oscillations in said load circuit at the termination of each pulse, and coupling means including a unilateral conducting device connected between said load circuit and said control electrode, said unilateral conducting device being disposed to render said. coupling means substantially non-responsive to load circuit voltages of said one polarity.

11. In combination, an electron discharge device including an anode, a cathode, and a control electrode, means including said control electrode for recurrently rendering said discharge device conductive for predetermined pulse intervals, a capacitive pulse-forming energy storing element, a load circuit connected to said capacitive element through said discharge device, said load circuit including an inductive energy storing element having a tendency to initiate voltage oscillations across said load circuit at the termination of each of said pulse intervals, and unilateral conducting coupling means for supplying said oscillations to said control electrode thereby to render said discharge device conductive to suppress said oscillations, said coupling means being substantially ineffective during said pulse intervals.

DONALD E. MAXWELL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,251,851 Moore Aug. 5, 1941 2,143,366 Andrieu Jan. 10, 1939 FOREIGN PATENTS Number Country Date 497,147 British Dec. 9, 1938 

